The present invention relates to indicator lights for computer systems and to testing for faults in an indicator assembly.
It is known to provide one or more indicators in a computer system which serve to indicate a functional state of the system by lighting up (or indeed, by remaining unlit). Typical functional states may include an on/off state, a fault state or an active state (for example whether a hard disk drive is active).
Indicators can comprise a light source and a guide for guiding light away from the light source, for example to the exterior of the computer system so that it is visible to the user. For example, an indicator can comprise a light emitting diode (LED) with a plastic cap. The cap itself may be positioned in an aperture in an exterior housing of a computer system so the user is able to determine whether the LED is lit. In some systems, a separate light guide is used to guide light from the LED to (and through) an exterior panel of the computer system. Such light guides are typically employed when the LED is located remote from the exterior panel.
Indicators are of particular use in computer systems which employ Field Replaceable Units (FRUs). FRUs in computer systems are typically provided in order to increase reliability the of the system by reducing the amount of downtime incurred when faults occur. Since a computer system comprising FRUs is essentially modular, a fault in the system can often be cured by simply replacing the particular FRU which contains the fault.
In computer systems comprising FRUs, indicators can provide an effective way in which functional states of each FRU may be readily ascertained, namely by inspecting the exterior of the FRU. This is particularly true in systems which comprise a large number of FRUs.
In the case of some applications, indicators may spend much of the time unlit. For example, where an indicator is intended to become lit only when a fault in a computer system arises (thereby alerting the user), indicators may only very rarely become lit if such faults seldom develop. Accordingly, a malfunction in the indicator itself may go unnoticed for some time. Additionally, should an indicator develop a fault, then the event or state which it is intended to indicate may go unnoticed or may be falsely determined by the user. For example, an active state may be misread by the user to be an inactive state.
Faults in an indicator may arise for a number of reasons. An LED comprised in the indicator may malfunction for example. Alternatively, a light guide connecting the LED to an exterior panel of the computer system may become loose or be dislodged (this is particularly prone to occurring during assembly of the computer). Where the light guide becomes dislodged, the indicator can fail even though the LED light source remains functional, since light emitted by the LED may not be transmitted to the exterior of the computer housing.